Solid phase assays can be performed in a number of different formats. Many of the currently available systems utilize a noncompetitive or sequential binding format.
For example, in the case of immunoassays, antibody is bound to a solid phase surface either by nonspecific adsorption or by a covalent attachment. The clinical specimen or tissue culture fluid is added to the solid phase and, following sufficient periods of time for reaction, is removed by means of a washing procedure. A second antibody is then added which will react with antigenic sites which are present on the added antigen but which have not been occupied by binding to the solid phase antibody. In some formats, this antibody is directly linked with the label. In such cases, the reaction is completed by washing unbound antibody and measuring the amount of label bound to the solid phase surface.
Alternatively, the second antibody can be added in an unlabeled form and its presence can be quantitated by the addition of another immunoreactant which will bind specifically with the second antibody (an indirect format). The second antibody can also be labeled with a nonenzymatic moiety and the reaction can be quantitated by the addition of reactant which will recognize that moiety specifically, e.g., streptavidin-biotin immunoassay. In all cases unreacted labeled antibody is removed by washing and the amount of label bound to the solid phase is determined by the appropriate instrumentation.
U.S. Pat. No. 4,656,143, issued to Baker et al. on Apr. 7, 1987, describes a heterogenous binding assay in which a liquid component and a granular particulate solid phase are incubated together for a predetermined period of time characterized in that the density of the liquid component is maintained substantially equal to the density of the granular particulate solid phase at least during the predetermined period of time. The density of the liquid component is maintained substantially equal to the density of the granular particulate solid phase by the addition of a density modifying medium having a density greater than the density of the granular particulate solid phase.
U.S. Pat. No. 4,914,023, issued to Philo on Apr. 3, 1990, describes a method of extending the linear range of an enzyme immunoassay by measuring off-peak absorbance.
European Patent Application Publication Number 288,179 published on Oct. 26, 1988 describes a method for detecting the MB isoenzyme of creatine kinase in a biological fluid which comprises (a) forming a mixture of a sample of biological fluid, an immobilized antibody to the B monomer of creatine kinase, and a labeled monoclonal antibody to the MB isoenzyme of creatine kinase; (b) incubating the mixture; (c) separating the solid support from the mixture; and (d) detecting the amount of label associated with the solid support.
U.S. Pat. No. 4,098,876, issued to Piasio et al. on Jul. 4, 1978, describes a reverse sandwich immunoassay which involves incubating a fluid with labeled antibodies to the analyte to be detected to form a labeled antibody-analyte complex and then incubating that complex with immobilized antibodies to the analyte to form a label antibody-analyte-immobilized antibody complex which is separated from the incubation medium.
U.S. Pat. No. 4,244,940, issued to Jeong et al. on Jan. 13, 1981, describes a two-site immunoassay in which the sample containing the analyte, a labeled receptor for the analyte, and an unlabeled receptor bound to a solid phase support are incubated together in an aqueous medium to form a substantially stable suspension. The solid and liquid phases are separated and either phase analyzed for the labeled receptor, the concentration of which is a function of the concentration of ligand in the sample.
UK Patent Application Number GB 2 190 490 A published on Nov. 18, 1987 describes an enzyme immunoassay in which an immune complex is obtained by simultaneously reacting the antigen, an immobilized first antibody and a second antibody with an enzyme-labelled third anti-second antibody, separating the solid phase from the liquid phase, and measuring the amount of enzyme activity present in the solid phase.